Amyotrophic lateral sclerosis (ALS) is an adult-onset, rapidly progressive and ultimately fatal neurodegenerative disease caused by the selective loss of motor neurons. Although most ALS cases are sporadic (SALS), ~10% are familial (FALS). To date, the underlying cause has been identified in only ~35% of all FALS cases: 20% are caused by mutations in SOD1, 5% in TARDBP and 5% in FUS. Variants in several other genes have been found in additional families to a lesser degree. Genetic studies have provided invaluable information for understanding of the pathogenesis of both FALS and SALS. Undoubtedly, the discovery of novel FALS- associated genes will dramatically further our knowledge of the cellular pathways that lead to motor neuron degeneration. Until now, it was not economically feasible to screen for rare variants at a genome-wide scale within disease-affected samples. However, the recent advances in automated, short-read DNA sequencing offer new solutions to this problem: it is now possible to sequence only protein-coding regions of the genome (exomes) to reduce costs while enriching for the discovery of highly penetrant variants. The purpose of this proposal is to identify novel causative genes for FALS using the approach of exome capture followed by short- read sequencing. The Specific Aims of this proposal are to: (1) Perform exon capture and short-read sequencing of selected samples to identify candidate FALS-specific variants. Exome capture and short-read sequencing will be performed for 2 distantly-related affected members of 10 ALS afflicted families (20 FALS). A primary list of candidate variants causative for ALS will then be created using a series of bioinformatic filtering steps. (2) Identify the variants derived from exome sequencing that are specific for FALS. Candidate variants will be interrogated by genotyping a panel of ~1,100 control samples as well as an additional panel of ~200 FALS. Variants detected in FALS, but not within the control population, are highly suggestive of a causative change. (3) Determine if candidate FALS genes show different mutations in additional FALS families. Candidate genes harboring FALS-specific variants will be sequenced in ~200 FALS samples to identify additional variants. Genes with multiple alterations in FALS not observed in control populations will be considered causal. Our proposed studies will identify novel candidate genes whose mutations cause FALS. In the long term, understanding the genetic causes of ALS will facilitate our understanding of all forms of ALS as well as assisting in the development of diagnostics and therapies to extend the lifespan of ALS patients.